1. Field of the Invention
The present invention discloses a method and apparatus for the transport of a homogeneous mixture of (chopped) fibers from a fiber generation source, such as a chopper gun, through a long flexible conduit to a workpiece. The transport apparatus is designed to eliminate nonhomogeneous flow of the fibers even as the conduit is maneuvered, so as to allow even deposition of the fibers on the workpiece.
2. Description of the Prior Art
Various manufacturers of nonwoven fabrics for use in glassfiber/resin composites have developed various apparatus for formation of these nonwoven fabrics or fiber "preforms". Reference for example Great Britain patent specification 659,088 of West Point Manufacturing Company, which teaches the removal of fibers from a fiber source by an air current, the passage of the fibers through a fixed transfer duct to a foraminous fiber-receiving member to form thereon a web of closely matted fibers, and the removal of the web from the member. The apparatus is designed to produce a two-dimensional fabric of constant thickness and width.
Reference also Great Britain Pat. No. 791,976 to Owens Corning Fiberglass Corporation wherein a fixed duct system supplies chopped fibers for their eventual deposition upon a preformed screen.
U.S. Pat. No. 3,833,698 discloses a movable chopper gun and roving cutter positioned within a rotatable preform, so as to allow even or uneven fiber deposition about the surface of the preform.
Reference also U.S. Pat. No. 4,117,067 issued Sept. 26, 1978 to Kenneth F. Charter et al; assignee, Owens Corning Fiberglass Corporation, entitled "High Production Method of Producing Glass Fiber Resin Composites and Articles Produced Thereby". Such an apparatus described in this '067 patent includes a device wherein air flow is introduced as a curtain along the sidewall of an inlet plenum, so as to assist the transport of fibers vertically downward through a fixed transport tube to their collection position. Such an apparatus incorporates a fiber chopper device at its inlet thereof.
Manufacturers of fiber reinforced plastic articles of manufacture continually attempt to improve the directed fiber placement process, wherein a chopper gun is used to generate chopped fibers, the fibers thereafter being deposited upon a workpiece. Boating manufacturers have typically used chopper gun technology during the manual layup or fabrication of boat hulls. Due to the lack of repeatability when the chopper gun is held manually, these manufacturers have attempted to automate the process by use of robotic equipment.
For example, a report entitled "Equipment Development and Feasibility Study of an Automated Preform Manufacturing System" was presented on Nov. 20, 1989 by D. M. Perelli of General Motors Corporation Advanced Engineering Staff, in which were described three different robotic/chopper gun systems, (hereinafter System 1, System 2, and System 3), which were operated to determine the feasibility of a robotic chopper gun system.
Referring now to FIG. 1, the apparatus shown as System 1 was used to produce door panel preforms. These preforms were of acceptable glass densities to meet the specifications for molding operations but the glass thickness was not uniform throughout the door panel preform.
The glass fibers deposited on the screen also exhibited a tendency to form ridges, the ridges being caused during various combinations of chopper fan shape, spray path followed by the robot, and various distances that the chopper gun held away from the preform screen. The System 1 stationary binder spray guns were ineffective in fully wetting out the glass.
Referring now to FIG. 2, the System 2, apparatus was used to produce both door panel and motor side compartment preforms. The System 2 apparatus was capable of spraying-up horizontally-mounted door panel preforms of exceptional uniformity as well as sufficient glass density. Glass fibers discharged from the flexible transport hose in a swirling pattern. This swirl-mixing within the hose made the glass discharge from the hose uniform in density. As a result, the fiber application to the horizontally-mounted door preform was uniform.
The vertical walls of the motor side compartment preform were difficult to spray uniformly, however, since the flexible transport hose had to be bent at the robot wrist to apply glass to the vertical walls of the screen. This bent portion of the hose apparently caused the glass fibers within the hose to stratify or lump together. Not surprisingly, the vertical walls of the finished preform showed signs of ridging. The System 2 assembly also did not offer a high degree of maneuverability due to the bulkiness of the flexible hose, which also made programming difficult, especially for continuous path programming. Movement of the robot wrist was also severely limited.
Referring now to FIG. 3, the System 3 apparatus was used to produce motor side compartment preforms which had correct and uniform glass fiber thickness. The preforms also exhibited the high degree of strength necessary for reaction injection molding, as well as the stiffness and strength needed for typical handling methods.
System 3 incorporates the best characteristics of Systems 1 and 2. Glass sprayed onto the three-dimensional screen was random and uniform across the preformed surface. No ridging was evident along the spray paths followed by the robot. Because the chopper gun could be pointed in any direction without bending the tube, no stratification of the glass fibers was evident in the discharge from the tube. Binder application was very good, and preform saturation was readily achieved. Overspray of glass on an average preform spray-up was less than 2%. This system was more mobile than System No. 2 though it was a bit less mobile than the System No. 1 design due to its added length.
Though System No. 3 performed the best this system as designed would burden the operator with large capital expense requirements, due to the large size of the robot required to lift and move the heavy chopper gun mounted at the end of the robot arm. The weight of the chopper gun held at the end of the robot arm requires an expensive robot having large lift capabilities.
An apparatus therefore need be developed, along with a method of operation, that allows the robotic application of chopped fibers to a workpiece of any orientation, wherein the lift capacity of the robot is minimized, and therefore its expense, by the remote location of the chopper gun away from the end of the arm of the robot. Such a system to be operative must avoid the fiber-clogging problems of System 2.